An organic electroluminescence (hereinafter referred to as “organic EL”) display device includes light emitting elements respectively corresponding to pixels, and individually controls light emission of the pixels to display an image. The light emitting element includes an anode, a cathode, and a layer containing an organic EL material (hereinafter also referred to as “light emitting layer”) sandwiched between the anode and the cathode. When electrons and holes are respectively injected from the cathode and the anode into the light emitting layer, the electrons and the holes are recombined with each other. By excessive energy released thereby, light emitting molecules included in the light emitting layer are excited, and are then deexcited, to emit light.
In the organic EL display device, the anode and the cathode of each of the light emitting elements are respectively provided as a pixel electrode for each of the pixels and provided as a common electrode to which a common potential is applied across the plurality of pixels. The organic EL display device controls the light emission of the pixels by applying a potential of the pixel electrode for each of the pixels to the potential of the common electrode.
In recent years, a foldable flexible display device has been actively developed. A support substrate in the flexible display device is easily cracked because a stress is concentrated on a folded site.
For example, Japanese Patent Application Laid-Open No. 2009-177071 discloses a polyimide film circuit board and a method of manufacturing the same. Thus, a metal wiring circuit pattern is formed on both surfaces or one surface of a copper-clad polyimide base material using a semi-additive method or a subtractive method. Then, the metal wiring circuit pattern portion is reinforced by being coated with heat-resistant insulating resin. Further, when a polyimide base material portion where a metal wiring circuit is not formed is thin-filmed by chemical etching, a polyimide insulating layer having different film thicknesses in the same substrate is formed.
The invention discussed in the above-described document relates to an improvement in processes for mounting various types of components on a flexible printed circuit board. According to the present invention, only a portion of a base material is thinned so that high dimensional stability can be ensured even if the base material is thin while high adaptability to a junction electronic device or the like can be ensured. On the other hand, the present invention does not cover a foldable flexible display device.